Merrill a



Aug, 36% W32. M. A. You-rz PREPARING GLYCOLS Filed Feb. 7, 1950 El, [LLA W Patented Aug. 30` 1932 UNITED STATES PATENT OFFICEv MEBILILL A. YOUTZ, OF HAMMOND, INDIANA, ASSIGNOR TO STANDARD OIL COMPANY, F CHICAGO, ILLINOIS, `A CORPORATION OF INDIANA PREPABING GLYCOLS Application led February 7, 1930. Serial No. 426,717.

This invention relates to electrolytic processes of preparing glycols and it comprises a process wherein an aqueous solution of sodium hydroxide is saturated with an olefin gas and the resulting olefin solution electrolyzed; it further comprises processes wherein an aqueous solution of an appropriate electrolyte is saturated with an olefin gas under high pressure and the so saturated solution electrolyzed; and it additionally comprises processes wherein an olefin 1s dissolved under high pressure in a lycol solution containing an electrolyte an ythe olefin then converted to glycol electrolytically.

Most of the methods of preparing the glycols depend upon the hydrolysis of chlorhydrins by means of alkalies, p Such processes involve either the substitution o f a chlorine atom by hydroxyl or the conversion of chlorhydrins to olein oxides and the hydration of the latter to glycols. Electrolytic processes wherein olefins are converted to chlorhydrins have been described. It has, for instance, been suggested to pass ethylene into a solution of sodium chloride under oing electrolysis. Under properly control ed conditions it is possible to obtain ethylene chlorhydrin in this way. Suggestions are also found in the literature, patented and otherwise, that the lycols may be made directly from oleins y electrolytic processes.

As far as I am aware, such processes have not proven very satisfactory.

I have now found that the electrolytic oxidation of olefins to glycols is improved when solutions of caustic soda are chosen as the electrolyte and I have also found that the process is greatly enhanced if relatively high pressures are used. Either of these newly discovered expedients materially improve the electrolytic oxidation. I find it best to use them together but electrolysis of a caustic soda solution through which ythe olefin is passed at pressures but slightl in excess of atmospheric leads to accepta le yields of glycols. So also, electrolysis of other suitable electrolytes saturated with the olefin under high pressure gives improved results but generally, I prefer to use high pressures and 50 caustic soda solutions.

When using caustic soda solutions I may employ iron anode and cathode elements and this simplifies the design of the electrolytic cell. In the electrolysis of caustic soda solutions, hydrogen is liberated at the cathode as a result of the reaction .between neutralized sodium ions and water so that the liquor surrounding the cathode is continuously replenished with caustic soda as a natural result of the process. Hydroxyl ions, -migratin to the anode, are there neutralized and com ine to form water and oxygen. In the presence of an olefin, however, the neutralized hydroxyl ions react therewith to form glycols. T his means that in in process, I am, in ei'ect, reacting olefin gas with water to form glycol and hy rogen.

In carrying out my process, I find it most advantageous to dissolve the olefin gas in the electrolyte under high pressure and pass the solution of olefin gas, still under high pressure, to one orl more electrolytic cells. In the appended drawing, I have indicated the more general aspects of my process in semi-How sheet form.

In the drawing,

Figure l represents an assembly of suitable apparatus, the various elements thereof being indicated more or less diagrammatically, and

Figure 2 shows in cross-section, a suitable typel of cell I find useful.

Referring more particularly to Figure 1, olefin gas, which may consist of pure ethylene, propylene or butylene or mixtures thereof,or so-called still gases formed in petroleum refining operations, is conducted by pipelto a pump 2 wherein it is compressed to a pressure of 20 to 200 atmospheres, roughly 300 to 3,000 pounds per square inch. The compressed gas enters the lower end of an absorption tower 3, provided with baiile plates as shown schematically. Other devices to insure eliicient contact between liquids and gases can, of course, be used. An aqueous solution of an electrolyte coming from a source of supply through 4 is pumped into the top of the tower 3 by means of pump 5 and pipe 6 controlled by valve 6a. The pressure on the electrolyte must of course be above that within the tower.

A vent ipe 7 at the top of the tower permits undissolyed gases to escape. Liquid collecting in the bottom of the tower will consist of an aqueous solution of electrolyte containing dissolved olefin gas under pressure. This solution is drawn from the tower by means of pipe 8 controlled by valve 8a and is passed to the electrolytic cells 9 shown as a bank of six. The outlets, 11, of each cell are connected to the inlets 10 of each succeeding cell. Suitable electrical connections to the cells are indicated by the bus bars 13 and 14. As shown, the saturated solution of olefin gas and electrolyte passes through the series of cells and leaves the last by pipe 15. The solution leaving the last cell consists of an aqueous solution of glycol and electrolyte and usually I pass this solution by valve 16 to suitable evaporators wherein the glycol is recovered. However, I sometimes find it advantageous to recycle a part or all of the crude glycol solution and this I do by by-passing a part of the crude glycol solution back to the top of the tower through pipe 18 controlled by valves 17 and 20 and the pump 19.

In Figure 2 I have shown a type of cell which I have found suitable for use in my process although there are a great many different types of cells which I can us. Ido not restrict myself to any one type since cells for the electrolysis of caustic soda solution may take many forms.

The cell shown in Figure 2 consists of a steel container 9 having an inlet 10 and outlets 11. The electrode elements 23 and 24 may be of iron. They may be separated by a. porous diaphragm 25, which is preferably 0f sufficient porosity to permit limited mixing of the solution in the two compartments, as well as equalization of pressure. However, a diaphragm is not essential to successful operation. The hydrogen which is evolved at the cathode 23 is conducted from* the cells by vent pipe 21 controlled by valve 22 which is adjusted to permit the discharge of the hydrogen at about the same rate at which it is evolved at the cathode. Some olefin gas is carried along with the hydrogen, especially in the first cells, and I find it advantageous'to pass the escaping gases to a tower wherein they be contacted with alcohol or other'preferential solvents for the purpose of dissolving and recovering such oletins as are carried away with the hydrogen. Hydrogen itself is much less soluble in alcohol than are the olefins.

More specifically, and in one exemplification of my process, When I wish to make ethylene glycol, I compress the ethylene to a pressure of 20 to 200 atmospheres and pass the compressed ethylene into tower 3 wherein it comes into contact with a caustic soda solution of about 25% strength. There is nothing very critical about the strength of the electrolyte. Of course the higher the concentration thereof, the less electrical resistance will the cell have. But as the concentration of caustic soda solution is increased the solubility of ethylene therein decreases somewhat. A caustic soda solution of about 25% concentration gives me good electrical conductivity and about normal solubility of the ethylene in Water under the prevailing temperature and pressure conditions. It the concentration of electrolyte is materially increased the resulting saving in electrical efficiency, because of lessened electrical resistance is overbalanced by the decreased solubility of the ethylene.

lVheu saturating the electrolyte With ethylene or other olefin gas, and in the subsequent electrolysis, I find it best to keep the temperature at ordinary room temperature, say about 2Oo C.

I then pass the saturated solution of ethylene to the tirst electrolytic cell by way of valved pipe 8 and as the solution flows through the series of cells, the'ethylene vis converted therein to ethylene glycol. In the operation of the cells, the voltage should be about 2 to 21/2 volts and the current density is about 20 amperes per square decimeter. Actually the current density may vary over a wide range without affecting the chemical reaction. From an is desirable to keep down the current density to increase efficiency, but this is balanced against a lower capacity. The optimum value will vary with each installation.

The pressure is, of course, maintained on the solution during the passage thereof through the cells. As the ethylene becomes converted to glycol, the pressure changes somewhat with the absorption of ethylene and the evolution of hydrogen. Although the rate at which the solution fiows through the cells may be controlled so that the solution leaving the last of the series is substantially olefin free, in the interest of higher efficiency it is found undersirablc to carry the electrolysis this far in a single stage.

'Ihe solution leaving the last cell is conducted to a suitable evaporator wherein the glycol is recovered. A part or all of the crude glycol solution can be recirculated back to the tower 3. Since the electrolyte itself, that is, caustic soda, is being continuously regenerated at the cathodes during the electrolysis, no additional electrolyte need be added to the crude re-circulated solution. By re-circulating a part or all ot the crude glycol, can increase the concentration of the glycol in the crude liquor prior to sending it to the evaporators.

I find it most advantageous to work at relatively lngh pressures. At 200 atmospheres,

for example, ethylene is soluble in water to the extent of about 28 grains per liter whereas under ordinary atmospheric pressure conditions and at about 20 C. ethylene is soluble operating standpoint it to the extent of about 0.14'grams per liter. In other words, when working at high pressures I am enabled to increase the amount of ethylene available for reaction -purposes in any unit volume of solution 200 fold. Indeed, my process is essentially one occurring in a true liquid phase. .The only ethylene I have present is that which is in the dissolved state. I avoid having gaseous ethylene present and this is incontradistinction to prior processes wherein gaseous ethylene has been bu'bbled under atmospheric pressure or pressures slightly above, pas-t the anode of an electrolytic cell. When using pressures in the neighborhood of 200 atmospheres, the crude glycol solution leaving the cells contains upwards of 62 parts of glycol to 1000 parts of solution, in other words a concentration of about 6%. It the pressure is but 100 atmospheres, the glycol concentration in the crude solution amounts to about 3%. But even at pressures as low as 20 atmospheres, which I construe to be high, improved results are obtained. Working in a strictly liquid phase leads to high electrical efiiciency and high yields of glycol with no by-products and this is undoubtedly due to the fact that at all times the ethylene or other olefin is substantially dissolved in water and I am not depending upon any reaction between a gas and a liquid reagent. Also since the concentration of dissolved ethylene is relatively very large compared to` a low pressure process there is practically no tendency to further oxidize glycol to aldehydes, acids and CO2. This is serious for low pressure processes and compels resort to extreme agitation to keep an excess of ethylene dissolved in the electrolyte in contact with the anode and to very low anode current densities to avoid local depletion of ethylene.

The process I have more specifically disclosed is continuous since ethylene gas or other olefin gas is continuously passed into the tower 3 and a solution thereof` in the electrolyte` is continuously withdrawn and continuously passed through the cells. Of course, if desired, the process can be rendered discontinuous and in this event I simply prepare a saturated solution of ethylene or other olefin in 'the electrolyte and pass the solution to a suitable cell wherein electrolysis 1s effected. y

Throughout the process I prefer to work at temperatures not greatly in excess of ordinary room temperature, 20o-25 C. and it is somewhat advantageous to work at temperatures in the neighborhood o C. since at the lower temperatures the solubility of the olefins in water is increased.

When using high pressures, electrolytes other than solutions of caustic soda may be used, so long as the elcctrolytic reaction of the cathode is one liberating oxygen, and imc5 proved results are had because of the high pressures employed. However, I find that the best results are secured when high pressures are used in conjunction with caustic soda or other alkali metal hydroxide solu- C. pure propylene condenses to a liquid and when using mixed olefin gases, pressures slightly below the liquefying pressures of the mixture are best used. However, some slight liquefication of the olefin is not objectionable since when it liquefies the liquefied portion is more or less disseminated throughout the solution of electrolyte. Very high pressures far in excess of the liquefying pressure should be avoided if there is any tendency for the higher olefins to separate out in liquid layers. This tendency is not only dependent upon the actual pressures but is also determined somewhat by the concentration of the higher olefins in the gases being treated.

A single cell may of course be employed rather than a plurality of cells and material other than iron can be used for the electrode elements. Generally speaking, I find that what is good practice in the electrolysis of caustic soda solutions to form oxygen and hydrogen is good practice in the electrolysis of caustic soda solution saturated with olefin gas to form glycols and the particular arrangement of apparatus and design of cell is governed partly by prior practice with respect to the ordinary electrolysis of caustic soda solutions.

I find that my process is commercially practical even though the actual current efficiency may drop to or even lower. This is because, in general, electrolytic processes are more satisfactory, in that high yields without the formation of undesirable y-products are obtainable. I have found no occasion to employ a catalyst of an oxygen carrier type although such catalysts have been proposed as adjuncts in electrolytic processes. Since, in my process, I am working substantially in the liquid phase, the reaction is enormously speeded up because of the higher concentration of olefin in the oxidation zone, and ordinarily no catalysts are necessary. However, I do not mean `to exclude the use of catalysts from the scope of my invention should it be desirable to add one or more of such substances to the electrolyte prior to or during electrolysis.

What I claim is:

l. In the process of preparing glycols from olefins electrolytically, the step which comprises electrolyzing an alkali `metal hydroxide T.;

fw.. has

solution containing olefin dissolved therein under high pressure.

2. In the process of preparing ethylene glycol from olefins electrolytically the step which comprises electrolyzing an alkali metal hydroxide solution Containing ethylene dissolved therein under hi h pressure.

In the process o? preparing ethylene glycol from ethylene electrolytically, the step which comprises electrolyzing a sodium hydroxide solution containing ethylene dissolved therein under a pressure ofv 20 to 200 atmospheres.

4. The process of preparing glycols which comprises electrolyzing a solution of an alkali metal hydroxide containing dissolved olefin.

The process of preparing ethylene glycol which comprises electrolyzing a solution of sodium hydroxide containing dissolved l ethylene.

6. The process of preparing ethylene glycol which comprises electrolyzing a solution of sodium hydroxide and et ylene, the ethylene being substantially wholly dissolved in said solution.

'l'. The process of preparing glycols electrically which comprises saturating a solution ot' an appropriate electrolyte with an olefin under a pressure of at least 20 atmospheres so that substantially all of the olefin is in the dissolved state and any undissolved olefin is present in a liquefied condition, and the mixture is free of gaseous undissolved olefin, electrolyzing the so-formed mixture to convert the olefin therein to glycol, saturut ing at least a portion of the resulting glyvol solution with additional quantities of olefin. and again electrolyzing.

8. The process of preparing glycols electrolytically which comprises saturating a solution of sodium hydroxide with an olefin to form a solution containing the olefin in a substantially wholly dissolved state, electrolyzing the so-formed solution to convert the olefin therein to glycol, saturating at least a portion of the resulting glycol solution with additional quantities of olefin and again elec- -trolyzing 9. Theprocess of preparing ethylene glycol electrolytically which comprises saturating a solution of an appropriate electrolyte with ethylene under a pressure of at least 20 atmospheres so that substantially all of the ethylene is in the dissolved state and Aany undissolved olefin is present in a liquefied condition, and the solution is free of gaseous undissolved ethylene, electrolyzing the soformed solution to convert the ethylene therein to glycol, saturating at least a portion of the resulting glycol solution with additional quantities of ethylene, and again electrolyzmg. 10. The process of preparing ethylene glycol electrolytically which comprises saiturating a solution of sodi um hydroxide with Arating at least solution of an appropriate ethylene to form a solution containing the ethylene in a substantially wholly dissolved state, electrolyzing the sO-formed solution to convert the ethylene therein to glycol, satua portion of the resulting lycol solution with additional quantities of hylene, and again electrolyzing.

11. In the process of preparing glycols from olefins electrolytically, the steps which comprise dissolving an olefin in an aqueous electrolyte under a pressure of at least 20 atmospheres so that substantially all of the olefin is in the dissolved state andany undissolved olefin is present in a liquefied condition, and the solution is free of gaseous, undissolved olefin, and electrolyzing the so-prepared solution.

12. In the process of preparing glycols from olefns electrolytically, the steps Which comprise dissolving ethylene in an aqueous solution of an appropriate electrolyte under a pressure of at least 20 atmospheres so that substantially all of the ethylene is in the dissolved state and the solution is free of gaseous, undissolved ethylene, and electrolyzing the so-prepared solution.

13. The process of preparing glycols from still gases electrolytically which comprises preparing an aqueous mixture of an appropriate electrolyte and still gas oletins wherein substantially all of the olefin is in the dissolved state and any undissolved olefin is in liquefied condition, and the solution is free of undissolved, gaseous olefin, and electrolyzing the so-prepared solution.

Signed this 28th day of January, 1930, at Whiting, county of Lake, State of Indiana.

MERRILL A. YOUTZ. 

